Domestic wastewater is conventionally treated via primary, secondary and tertiary process before disposing or recycling. Chemically enhanced primary treatment (CEPT) process has been implemented as an alternative treatment process to the conventional process for domestic sewage. As large quantity of wastewater is rapidly treated in this process, CEPT process is greatly useful for rapidly-growing mega cities and developing countries. The CEPT plant located at Stonecutters Island, Hong Kong is one of the biggest CEPT plant in the world, which treats 1.4 million m3 sewage per day. Typically the CEPT process is used to treat the sewage using inorganic trivalent flocculants, generally ferric chloride, followed by the anionic polymer for removal of suspended solids from the wastewater. After the polymer treatment, the flocculated sewage is allowed for settling of suspended solids particles. The settling process leaves a huge quantity of the sludge which contains a water content of >95%.
The primary sludge contains a bulk volume of water and suspended particles. The solids content of the CEPT sludge ranges around 2˜4% by weight. For safe disposal or further utilization of the primary sludge, the sludge solids must be removed from water and stabilized. Dewatering of the sludge is essential that can be achieved by mechanical dewatering process through filter pressing or centrifugation after appropriate preconditioning of sludge. Due to the high strength suspended particles having high negative charge, the CEPT sludge is difficult to dewater and it needs to be conditioned with very efficient flocculants to improve the dewaterability.
The inorganic metal flocculants and organic polymers are generally used as pre-dewatering conditioning agents. However, due to the requirement of large quantity of inorganic flocculants, sludge management itself is an expensive process in sewage treatment. Excessive FeCl3 would cause more serious issue. In sludge dewatering process, the typical doses of polyelectrolyte polymers between 1-10 kg per metric ton of dry sludge solids are used, and the polymers thus accounts for 0.1% -1% of the total dry solid mass of a conditioned sludge. Requirement of huge quantities of the expensive flocculants itself covers about 50% cost of the sludge treatment process. In addition, some cationic organic polymers used to enhance thickening and dehydration processes could result in strong odors due to their degradation during the storage of dewatered sludge. Moreover, polymeric flocculants and their derivatives, pose a number of ecological hazards as some of the derivatives are non-biodegradable and the intermediate products of their degradation are hazardous to human health as their monomers are neurotoxic and carcinogenic. Therefore, environmental-friendly and safe coagulants need to be developed for sludge dewatering.
To alleviate the concerns over the use of synthetic flocculants, currently, biogenic flocculants are drawing increasing attention due to their satisfied flocculating effectiveness and safe biodegradable nature. Biogenic flocculants are the inorganic and organic flocculants derived from microbial cultures as a whole or their products. Microbial bioflocculants have been demonstrated for potential removal of suspended solids, chemical oxygen demand (COD), and heavy metals from several wastewaters, including domestic, brewage and pharmaceutical wastewaters. Most of the microbial bioflocculants reported are polysaccharides, which are mainly involved in coagulation/flocculation process via bridging mechanism only. On the other hand, biogenic ferric iron produced by acidophilic iron-oxidizing bacteria can also be used as potential coagulant/flocculant for sludge dewatering.
The present invention provides a novel composite biogenic flocculant using non-hazardous and low-cost commercially available chemicals, naturally occurring microbes and renewable waste materials and method of manufacturing the same. The present composite biogenic flocculant comprises both autotrophic and organotrophic microbes that produce strong flocculants. Autotrophic microbes employed in the present invention are acidophilic bacteria that obtain energy from iron containing substrate and elements that contain sulfur, and a consortium of organotrophs isolated from organic wastes. The present method of manufacturing a composite biogenic flocculant involves the use of autotrophic and organotrophic bacteria and less expensive divalent iron source, and rapid production of flocculant. The composite biogenic flocculant rapidly improves the sludge dewaterability.
Citation or identification of any reference in this section or any other section of this application shall not be construed as an admission that such reference is available as prior art for the present application.